1. Field of the Invention
My invention relates to wafer probers, that is, apparatus for testing integrated circuits or electronic devices such as transistors and diodes which have been fabricated within and upon semiconductor wafers or thin slices of semiconductor material. More specifically, my invention deals with improved means for correctly orienting, or setting in a predetermined angular position, successive wafers on the table or turntable of the wafer prober prior to the testing thereof.
2. Description of the Prior Art
In wafer probers of the type under consideration, successive semiconductor wafers to be tested are loaded one at a time on the table which is both rotatable and movable linearly in any of three different directions each perpendicular to the other two. The wafer is tested by means of probes which are relatively moved into contact with preselected electrodes on the wafer. For establishing proper contact between the probes and the preselected electrodes on the wafer, the position of the latter must be precisely adjusted relative to the probes as by use of a microscope. This fine adjustment of the wafer position can be greatly facilitated if the wafer is previously properly oriented or set approximately in a predetermined angular position relative to the probes.
It has been suggested and practiced to so orient the successive wafers before they are loaded on the table. Each wafer has formed therein what is herein termed an orientation recess designed to facilitate such preliminary orientation. This conventional practice is objectionable, however, in that the wafers, once properly oriented, are very likely to suffer angular displacement by the time they are mounted in position on the table. Another objection is that the wafers are susceptible to warpage or other damage as they are oriented by means which are forced into direct contact therewith.